A growing trend within the electrical device industry is to enable previously stand alone electrical devices, such as sensors and lighting control devices, to communicate with each other over some type of communications network. Previously, sensor, switch and control devices communicated using point to point connections. Nowadays, manufacturers are building into these devices communication means to enable them to communicate over local area networks (LANs). A variety of systems are currently commercially available which electrical device manufacturers can integrate into their products to enable them to communicate over a network.
One such system is the CEBus system which has been made an EIA standard, the EIA 600 standard, and was originally developed by Intellon Corp. A second system is the LonWorks system commercially available from and developed by Echelon Corp. Both the CEBus and LonWorks systems specify physical and link layer means for communicating over a variety of different media including power line, coaxial cable, fiber optic cable, radio frequency (RF), infrared (IR) and twisted pair cable.
For example, in the area of lighting, it is possible to wire an electrical load to multiple switches such that turning any of the switches on functions to turn the load on. The wiring circuits for two and three way switches are well known and relatively simple to implement. As the number of switches increases, e.g., four way, five way and beyond, the wiring circuits become extremely complicated and unwieldy.
Utilizing one of these systems makes it much easier to design electrical systems which comprise a plurality of different sensing and control devices. Using the lighting example presented above, it is a straight forward application to implement a lighting system whereby multiple sensors or switches control the same lighting control device. For example, each device within a mixture of multiple occupancy sensors, switches or other types of sensor/switch devices can be configured to activate and control the same lighting control device.
However, a disadvantage is when maintenance or service is required to be performed on any of the input sensing or dimming devices controlling or connected to the same lighting control device. Although one of the devices is disabled or placed in an off mode, any of the other devices is still free to activate the application of electrical power to the load.